This invention relates to a paint detackifier and sedimentation agent based on nanocrystalline or amorphous aluminas and/or alumina hydrates.
When applying lacquers, waxes, or similar coating materials containing organic substances which are not soluble in water, it sometimes happens that not all of the material reaches the intended article to be coated. Especially when painting automobile bodies, oversprayed paint deposits in the paint spray booths. The lacquer or paint mist formed in these booths when spray painting goods, such as automobile bodies, is scrubbed by an air-flow which makes the overspray contact recirculated water or a water curtain, or it is removed by other paint mist wet separators. In order that no tacky paint residues agglomerate in the scrubbing system and plug the mist eliminators, spray heads, and recirculating pumps, detackifiers and sedimentation agents are employed to make the paint particles coagulate in the wash water and precipitate. It is desirable to obtain in a single work cycle a non-tacky and easily removable sludge.
Up to the present, many different additives have been tried as flocculants, detackifiers, or coagulants. For instance, it is known to use inorganic additives containing aluminium, such as aluminium silicates, aluminium sulfates, aluminium chlorides, aluminium oxides, aluminium hydroxides, or montmorillonites. In addition, a large number of organic auxiliaries are known which can be employed alone or in combination with the aforementioned inorganic additives, for example polyacrylamides, polymethacrylates, polyvinyl alcohols, polyalkylene oxides, starch, or cellulose.
The use of montmorillonites or smectite in combination with marble lime hydrate and cellulose as a paint detackifier is disclosed in DE A-34 21 270. U.S. Pat. Nos. 4,564,464 and 4,504,395 disclose detackifiers for high-solids paints which contain bentonite, particularly hectorite, as a main component and are blended for economic reasons with montmorillonite clays or alumina and which also contain the usual additives, such as foam depressants and coagulants.
The disadvantages of all prior art paint detackifiers are their different effects on the different types of lacquers, such as NC, polyacrylate, polyester, or PU lacquers, and waxes. Furthermore, when employed for the widely used high-solids lacquers, said detackifiers are inefficient because quantities of up to 50 wt. %, based on the weight of the sprayed paint, are required to perform the detackification.
DE 38 17 251 (EP 0 342 339) suggests the use of paint detackifiers based on alumina (Al2O3) of the pseudoboehmite or boehmite type either in the X-ray amorphous form or with 2 to 15 nm size crystallites. It is reported in said patent that much smaller quantities are required in contrast to bentonite-containing detackifiers and that said system can be used as a one-component system or in combination with customary defoamers or polymeric deflocculants. The polymeric deflocculant Praestol 2415 (acrylamide/acrylate copolymer) manufactured by Stockhausen is disclosed in said patent.